Wireless communication networks facilitate communications with mobile or wireless user devices (often referred to as mobile subscribers, remote stations, or terminals). User devices may include cordless phones, cellular phones, satellite phones, pagers, computers, personal digital assistants (PDAs), entertainment devices, combined function devices, etc. Wireless network equipment (e.g., base stations) and user devices have been modified to use feedback information provided by the user devices to adjust future communications with the user devices in order to improve quality and throughput. One type of feedback information that is often used is referred to as channel quality (e.g., channel quality indication or index (CQI)), and may include information regarding the quality of the transmission channel. A user device measures the channel quality and provides feedback information to network equipment (e.g., via a reverse link). The network equipment (e.g., a base station) uses the feedback information for many purposes, such as selecting to which user device to transmit data (e.g., channel-dependent scheduling), selecting a transport format for user device (e.g., link adaptation), power-setting (e.g., a type of link adaptation), etc.
Link adaptation (or link quality control) is a well-known technique for adjusting transmission parameters (e.g., modulation, coding, transport block size, output power, etc.) to optimize use of a communication channel in terms of data throughput, delay, bit or block error rates, speech quality, or other performance measures. In order to perform link adaptation, feedback information about the communication channel (e.g., as experienced by a receiving device, such as a user device) is provided to a transmitting device (e.g., a base station providing the communication channel) on a reverse channel. Examples of such feedback information include a bit error rate, a block error rate (BLER), acknowledgement (ACK) and/or negative acknowledgement (NACK) information, power control commands, a carrier-to-interference ratio, a received signal strength, etc.
Feedback information most directly related to the channel quality (e.g., the carrier-to-interference ratio) are difficult to measure and are more uncertain than indirect feedback information, such as the block error rate. Hence, link adaptation schemes that track fast channel quality variations often use indirect feedback information to adjust direct channel quality reports, which are a primary basis for link adaptation. For example, a link adaptation scheme for high-speed downlink packet access (HSDPA) based networks may use ACK/NACK feedback information to modify CQI values (e.g., provided by channel quality reports) to achieve a specified long-term NACK rate. A link adaptation scheme for enhanced data rates for global evolution (EDGE) based networks may use ACK/NACK bit map feedback information in a similar way together with reported bit error probability (BEP) levels. Channel quality feedback information is also used for purposes other than link adaptation. For example, feedback information is used for scheduling in multi-user systems with shared resources to ensure that the shared resources are efficiently utilized. Feedback from the receiving device, such as block errors (e.g., ACK/NACK information), may be required if selective retransmissions are to be enabled.
Current mechanisms for transmitting channel quality feedback information, when fast channel variations are being tracked, have several disadvantages. First, the current mechanisms utilize substantial resources on the reverse link. Better link adaptation results and scheduling decisions are provided if more feedback information is provided. However, as more feedback information is provided, a greater burden is placed on reverse link resources (e.g., user device batteries). Thus, there is an undesirable tradeoff between link adaptation performance on a forward link and feedback information burden on the reverse link. In addition to capacity loss, a resource cost of transmitting feedback information has an adverse impact on reverse link coverage.
Current mechanisms for transmitting channel quality feedback information also scale poorly to multiple antennas, multiple data streams, and multiple frequencies, which are key features in the evolution of cellular networks (e.g., High Speed Packet Access (HSPA) and Long-Term Evolution (LTE) networks). Thus, current mechanisms for transmitting channel quality feedback information may place an unreasonable burden on both reverse link resources and scheduling and link adaptation processing in future networks.
When periodic reporting is used for providing channel quality feedback information (e.g., in HSDPA based networks), current mechanisms fail to provide a dynamic connection between the amount of generated channel feedback information and a need for such feedback information at the transmitting device. Attempts to address this disadvantage (e.g., with current mechanisms) by reducing the amount of generated channel feedback information negatively impacts link adaptation and scheduling performance.